THURSDAY, Feb. 28 (HealthDay News) -- About one in five U.S. adult smokers has used electronic cigarettes, a new study finds.

E-cigarettes are battery-powered devices that deliver nicotine, flavorings and other chemicals. They turn these substances into vapor that is inhaled by the user, which is referred to as "vaping."

In 2011, about 21 percent of adult smokers in the United States said they had used e-cigarettes, up from about 10 percent in 2010. About 6 percent of all adults have tried e-cigarettes, according to the U.S. Centers for Disease Control and Prevention (CDC) study released Thursday.

Between 2010 and 2011, the use of e-cigarettes among adult smokers rose among both men and women, whites, those aged 45 to 54, people living in the South, and current and former smokers, the study authors found.

In both years, e-cigarette use was much higher among current smokers than among former and never smokers, the investigators noted. Awareness of e-cigarettes increased from about 40 percent of adults in 2010 to 60 percent of adults in 2011.

"E-cigarette use is growing rapidly. There is still a lot we don't know about these products, including whether they will decrease or increase use of traditional cigarettes," Dr. Tom Frieden, CDC director, said in an agency news release.

Compared to traditional cigarettes, e-cigarettes appear to have far fewer toxins, according to the CDC authors. However, the impact of the devices on long-term health need more study, they noted.

Research is also needed to see how e-cigarette marketing could affect the use of traditional cigarettes, especially among young people, the authors noted in the news release.

"If large numbers of adult smokers become users of both traditional cigarettes and e-cigarettes -- rather than using e-cigarettes to quit cigarettes completely -- the net public health effect could be quite negative," Dr. Tim McAfee, director of the CDC's Office on Smoking and Health, said in the news release.